From oocyte retrieval to blastocyst cryopreservation, the best
timing to do fertilization is always an important issue in the IVF realm. The
techniques of ICSI, or IMSI, can help the embryo technician select the sperm with
the best morphology to increase the fertilization rate. After the development
of spindle microscope (an modified microscope which can observe the spindle of
oocyte), the question of "when to fertilize?" has emerged.

In the newly-released article of Science, the author explained the
reason of higher chromosomal aneuploidy in human oocytes in comparison with the
other human somatic cells, and mouse oocytes. Holubcova el al. developed a
time-lapse system combing with vital stain of human oocyte to record the oocyte
maturation process (from GVBD to MII).

They found that the time from GVBD (geminal vesicle breakdown) to initial
chromosome congression (~16 hrs) was significantly longer than those in the
other mammal meiosis (~3-5 hrs). Instead of mediating by centrosomes or MTOCs
(microtubule organizing centers), the mediator in human oocyte meiosis was
chromosome itself (Ran-GTP).

Lacking of centrosomes or MTOCs led spindle formation in human
oocytes intrinsically unstable and error-prone, and then it made the higher
aneuploid rate due to maternal origin in the following embryo propagation.

Of the application in IVF, this time-lapse video of oocyte
maturation may provide the users of spindle microscope more information about
the accurate timing to do the fertilization, or to cryopreserve the MII eggs.